If you ever try to discuss carbon emissions trading you are soon left feeling as if you're wading through a giant bowl of Alphabeti Spaghetti. The subject drips with acronyms: CDM, ROCs, EU ETS, CRC, EUAs, CERs. Rumour has it that some ministers have been known to carry cribsheets into high-level discussions to protect themselves against this blizzard of jargon - and who can blame them?

It can be such a, let's be frank, dull and impenetrable subject that there are those who believe the obfuscation is intentional, to repel prying eyes from exposing the murky workings of the only truly international system up and running that's designed, by curbing greenhouse gas emissions via the "cap and trade" principle, to protect us against runaway climate change.

Bryony Worthington, who has inhaled the fug of emissions trading every day for the past decade, first as an environmental campaigner, then as a government official, and finally as a lobbyist for a giant energy firm, has had enough.

Using her unique knowledge of how "this game" works, she wants to expose its underbelly and help to spark greater debate about what, she believes, is a vitally important component of our collective fight against climate change.

"Sunlight is the best disinfectant," she says, sitting inside her temporary new 'office', a corner in her local pub in north London. "If you open all this process up to the public and show them what's happening, then you stand a much better chance of cleaning this up."

Permits to pollute

Next week, Worthington launches Sandbag.org.uk, a not-for-profit website that allows members to buy up surplus "permits to pollute" that form the currency of the European Union's emissions trading scheme (or EU ETSs). Members can then "retire" them so that they cannot continue to be traded between the industrial polluters - cement, steel and car manufacturers etc - forced by EU regulation to operate within the system. "I suppose it's a bit like burning money in front of someone so they can't spend it on something bad," she explains.

The concept sounds like a clever variation of carbon offsetting, the now mocked method of allowing people to atone for their "carbon sins" - flying, driving, heating - by letting them pay for, say, a tree to be planted, or someone else, often in a developing country, to reduce emissions on their behalf.

Worthington is sensitive to the charge. "We've deliberately tried not to look like an offsetting website," she says, adding that some offsetting firms can, in her view, be "more evil than doing nothing" due to the often neo-imperialistic veneer of some of the offsetting projects they fund in the developing world.

"There's no carbon calculator on our site, for example. My pitch is simply that if you haven't got a lot of time, but do have a credit card, you can take, say, a tonne of carbon dioxide out of the atmosphere in a second by paying for an emissions credit to be withdrawn from the system." At the current rate of trading in the EU ETS, a tonne of carbon is priced at about €23 (£18), around twice the average price to offset a tonne of CO2 as charged by an offsetting company.

"I really want to distance Sandbag from the term 'offsetting'. Most schemes today are simply saying to someone in a country such as India, 'You can't use a diesel pump for your water hole. Use this hand pump instead because we're trying to get carbon emissions down'. So these people end up using a more labour-intensive device so that we can drive down to Sainsbury's to pick up some Evian? That's just wrong."

She sees Sandbag's role as offering a platform to help people subvert, agitate and campaign against the imperfections and injustices embedded in the current emissions trading scheme. She would far prefer to use the collective voice of future Sandbag members to coax the big industrial polluters into handing over their surplus credits than have to rely on members to buy them. But, I put to her, surely this is an idealistic dream? Why on earth would these firms with surplus credits - which Worthington estimates to be about two-thirds of the 300-odd firms currently operating within the EU ETS - wish to give up the chance to earn millions by selling them?

"We need to explain to these companies that they need a carbon market that works," she says, stressing that the current surplus threatens to kill the market dead, because the price remains far too low to encourage firms to implement meaningful reductions.

"What we have to tell them is that if the current system is allowed to fall over then the alternative will be a world of heavy regulation and high taxes. The allocation was calculated on nothing more than guesswork.

"They know the current surplus is a windfall. We know it's a windfall. Just give it back. We need to shame them into it by getting some forward-thinking firms to make the leap first."

Mould-breaker

It can be tempting to view Worthington as just another principled environmental campaigner: well intentioned, but hopelessly naïve to the motivations of those who sit in boardrooms. But her CV reveals plenty of experience of operating within the world of pin stripes and double strength lattes.

Worthington grew up on a farm in Wales. "I can remember doing talks at school about saving the whale. I wasn't a hippy, but I had a sentimental view of the environment."

After studying English literature, she travelled before joining Operation Raleigh as a fundraiser. It was in the mid-1990s, working for a conservation charity, that climate change pricked her consciousness. By 2000 she had moved to Friends of the Earth as a climate-change campaigner. But it was never a natural home for her.

"I didn't fit the mould at FoE. I was keen to talk to civil servants and talk about the detail of the policy. I've always been pragmatic. FoE is a great brand and has a brilliant media team, but I suppose it has quite a limiting perspective.

"Since going into government and the private sector I've noticed things aren't as black and white as you'd like them to be in the NGO world."

A spell at the Department for Environment, Food and Rural Affairs implementing public awareness campaigns and helping draft the Climate Change Bill, was followed by another career swerve. She became a lobbyist, "head of government relations", for Scottish and Southern Energy, one of the UK's largest energy companies.

For some former colleagues, this role reversal must have seemed as if she had not only danced with the devil but gone back to his place for the proverbial coffee. But her experience has given her a rare insight into the workings of three very different, yet interlocking, worlds.

"Working for the government can be amazing if you can get things going, but there's just so much inertia in the system," she says. By comparison, the private sector was "great". "People are motivated. Meetings are barely tolerated, whereas at NGOs everyone loves two to three-hour meetings. Government is even worse. In the private sector, I found a refreshing lack of politics."

But didn't she find it uncomfortable working for, as her campaigner friends might see it, the "enemy"?

"When I first walked in, they had pinned my old 'carbon dinosaur' campaigning leaflets to the computer screen to remind me that they knew where I had come from. But I wouldn't have gone there if I didn't think they were a forward-thinking company.

"I did think briefly, 'What have I done?' But in the time I was there, they invested massively in renewables and are one of the few energy companies working to help customers reduce their energy demand. They still do need to sort out what they are doing with coal, though. But then, no one really knows what to do yet."

Carrot and stick

Worthington says her time at Scottish and Southern Energy taught her that a market-based emissions reduction mechanism, such as the EU ETS, is the only option if we are ever to convince polluters to change. She welcomes the announcement by Gordon Brown on Thursday that the energy firms must help pay for homes to be better insulated, but says there are more important things the government could be concentrating on, such as carbon capture and storage (CCS) technology - the great, unproven hope for cleaning up coal.

"The government can't expect an incumbent industry to innovate towards CCS. Why would they change direction if they are making lots of money now? They need both a carrot and stick. The [emissions trading system], despite its problems, gives companies both. You need a market.

"You need to get capitalists interested - that's when you get big cash flow. Most people think we need credits to be worth €75 a tonne to get CCS off the ground. That's why we must fight to reduce the surplus."

But, she says, governments tend to be weak when facing the collective might of industry lobbyists. She hopes Sandbag will help individuals counter that.

"Having been a lobbyist myself you can't overstate how easy it is to get things done your way. In Brussels there is a key vote next month in which the Environment Council will begin deciding what it thinks the ETS allocations should be beyond 2013.

"Every industrial lobbyist worth their salt has been there all summer. By comparison, there are probably just five or so representatives from the NGOs. It's a complicated policy and many lobbyists are trying to wreck amendments as we speak.

"An NGO can't expect to win against this without some kind of major civil movement behind them. We have to target the educated, informed and affluent to do something. It's our responsibility, the ones who have all these privileges. That's what I'm trying to do with Sandbag."